Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating heart disease. This procedure generally entails introducing a catheter assembly into the cardiovascular system of a patient via the brachial or femoral artery, and advancing the catheter assembly through the coronary vasculature until a balloon portion thereon is positioned across an occlusive lesion. Once in position across the lesion, the balloon is inflated to a predetermined size to radially compress against the atherosclerotic plaque of the lesion to remodel the vessel wall. Subsequently, the balloon is deflated to allow the catheter assembly to be withdrawn from the vasculature.
While PTCA is widely used, it suffers from two unique problems. First, the blood vessel may suffer acute occlusion immediately after or within the initial hours after the dilation procedure. Such occlusion is referred to as “abrupt closure.” Abrupt closure occurs in approximately five percent of cases in which PTCA is employed. The primary mechanisms of abrupt closures are believed to be elastic recoil, arterial dissection and/or thrombosis. The second problem associated with this procedure is the re-narrowing of an artery after an initially successful angioplasty. This re-narrowing is referred to as “restenosis,” which typically occurs within the first six months after angioplasty. Restenosis is believed to be due to, among other things, the proliferation and migration of cellular components from the arterial wall, as well as through geometric changes in the arterial wall referred to as “remodeling.”
To reduce occlusion of the artery, and the development of thrombosis and/or restenosis, an expandable interventional device or prosthesis, one example of which includes a stent, is implanted in the lumen to maintain the vascular patency. Additionally, to better effectuate the treatment of such vascular disease, it is preferable to load an intraluminal device or prosthesis with one or more beneficial agents, such as antiproliferatives, for delivery to a lumen. One commonly applied technique for the local delivery of a drug is through the use of a polymeric carrier coated onto the surface of a stent, as disclosed in Berg et al., U.S. Pat. No. 5,464,650, the disclosure of which is incorporated herein by reference thereto. Such conventional methods and products generally have been considered satisfactory for their intended purpose. However, some problems associated with such drug eluting interventional devices is the variability in drug loading across an interventional device, as well as the variability in drug concentration from device to device. Other disadvantages include the inability to tightly control and maintain drug concentration, the inability to verify drug distribution or drug loading on any given device, the inability to vary drug distribution in a controlled and predetermined manner to effect a more desirable drug loading profile, the inability to load different, and in particular incompatible or reactive drugs onto the same surface of a device, and the difficulty in controlling the local areal density of beneficial agent that is delivered to the lumen, particularly if the interventional device is an overlapping or bifurcated device coated with beneficial agent.
As evident from the related art, conventional methods of loading interventional devices with beneficial agents, such as drugs, often requires coating the entire prosthesis with a polymer capable of releasing therapeutic drugs, as disclosed in Campbell, U.S. Pat. No. 5,649,977 and Dinh et al., U.S. Pat. No. 5,591,227, the disclosures of which are incorporated herein by reference thereto. Because certain interventional devices may have a varied surface area along its length, such conventional loading techniques results in unintentional or undesirable dosage variations. Additionally, if it is desired to superimpose two or more conventional-loaded prostheses, such as with nested stents or bifurcated stents, the total dosage of beneficial agent to the lumen will exceed the nominal or desired dosage. Another drawback of the conventional methods of loading interventional devices with beneficial agents is the lack of selective dosing, such as providing various beneficial agents or various concentrations of the same beneficial agent at different locations on a prosthesis to effect a therapy at specific targeted sites.
Thus, there remains a need for efficient and economic methods for controlling the loading of beneficial agent onto a prosthesis so as to provide an interventional device having a varied distribution profile of beneficial agent to effect therapy at targeted locations of the lumen. Additionally, there is a need for an interventional device capable of providing combination therapy of two or more beneficial agents loaded on different surfaces of a prosthesis to effectuate systemic release as well as release to the wall of the lumen. Further, a need exists for the loading of incompatible beneficial agents onto the same surface of a prosthesis. The advantages of the present invention satisfy the aforementioned needs.